This invention relates to a method and apparatus for controlling a throttle valve in an internal combustion engine so that the throttle valve driven by an electric motor can be opened and closed through an angle corresponding to the amount of depression of an accelerator pedal in a vehicle.
Control of open-close movement of a throttle valve in an internal combustion engine by means of an electric motor is already known from, for example, the disclosure of JP-A-61-129432 (1986).
According to the disclosure of the cited publication, a stepping motor is used to drive the throttle valve. Although the use of such a stepping motor for automatically controlling the open-close movement of the throttle valve is preferable in that the angular position of rotation of the throttle valve can be controlled with high accuracy, there is an inevitable tendency that the operation of the throttle valve is insufficient in its high-speed response capability.
A D.C. motor is preferably used in lieu of the stepping motor so as to ensure the desired high-speed response capability of the throttle valve. However, attainment of the desired high-speed response capability of the throttle valve driven by the D.C. motor tends to be affected by the factors of fluctuation which include: (a) changes in the coefficient of friction of the rotor shaft of the motor; (b) non-uniform spring constants of springs of throttle valves due to non-uniformity of the characteristics of manufactured products; and (c) secular variations (so-called permanent set) of the spring constant.
In order to solve problems as described above, an automatic control apparatus of highly advanced character adapted for self-tuning is required, resulting in an increase in the cost of its control circuit.
Also, an attempt to carry out automatic control by the use of a relatively inexpensive microprocessor will rather reduce the desired high-speed response capability of the throttle valve due to an inherent delay of arithmetic and logical processing.